Sepsis is a major cause of morbidity and mortality occurring in around 700,000 individuals per year in US. Acute lung injury (All) in patients with sepsis is common, and carries a high mortality (-40%). Adequate and timely neutrophil response to the site of infection could limit sepsis in patients, yet uncontrolled accumulation of these cells could also lead to end-organ damage, one of the major reasons for multiple organ failure, including ALL Chemotaxis of neutrophils to the site of infection or inflammation are essential to this process. In this proposal we are going to study the central role of matrix metalloproteinase (MMP)-8 in neutrophil chemotaxis in models of sepsis, ventilator-induced lung injury (VILI) and the combination of sepsis-induced lung injury with subsequent VILI. Our preliminary data suggests that MMP-8 limits the neutrophil chemotaxis into sites of inflammation/infection. This property of MMP-8 is deleterious in our sepsis model of cecal- ligation and puncture, where the MMP-8 deficient mice had a significant survival advantage. On the other hand, the lack of MMP-8 led to inappropriate accumulation of neutrophils in the lung tissues in mice on mechanical ventilation and led to significant VILI. The research proposal will serve as a training program for the applicant with a focus on MMP-8 biology in the setting of clinically relevant questions, a perfect fit for a candidate on the path of becoming a clinician-scientist. This application takes advantage of the diversity of resources available within the Department of Medicine and Critical Care Medicine at the University of Pittsburgh to provide the principal investigator with a unique training program designed to foster a successful research career under the mentorship of Dr. Steven D. Shapiro. The experimental approach is unique in that it utilizes a murine model of (i) extra-pulmonary sepsis, (ii) ventilator-induced lung injury, and (iii) the modulating effects of concomitant mechanical ventilation in the setting of sepsis-related ALI to study the role of MMP-8. Specific aims include: 1) mechanism of MMP-8 dependent bacterial clearance in a sepsis model, 2) role of MMP-8 in VILI, and 3) MMP-8 dependent cytokine inactivation, including proteomic approaches. Results are expected to yield fundamental insights into the MMP-8 biology in clinically relevant disease models and possibly provide the basis for development of novel anti-inflammatory therapeutic strategies for sepsis and ALI. Acute lung injury in the setting of systemic infection and inflammation such as sepsis carries a high risk for mortality. In this proposal, we will study a key molecule, namely matrix metalloproteinase (MMP)-8 in mouse models of sepsis, acute lung injury and the possible injury inflicted by the use of mechanical ventilation.